As disclosed in U.S. Pat. No. 5,887,221 to Grace; and U.S. Pat. No. 5,543,896 to Mestha; and U.S. Pat. No. 6,694,109 to Donaldson et al., the use of sensors in a xerographic engine to detect the toner mass levels on a photoreceptor, or other substrate, in a post-development position (detection of developed mass) is known. The use of sensors to detect residual toner mass levels post-cleaning device is also described in U.S. Pat. No. 6,272,295 to Lindblad et al. and U.S. Pat. No. 5,903,797 to Daniels et al. It is also known to measure the residual mass after transfer but before the cleaning device (post transfer residual mass).
Previous post-transfer residual mass sensors provided information about the average transfer efficiency and could enable limited closed loop control of a xerographic transfer system. For example, use of an Extended Toner Area Coverage (ETAC) sensor to measure residual mass during xerographic setup. The data from an ETAC sensor was used to adjust a transfer shield current set point to calibrate or adjust the system to obtain optimal performance prior to the submission of a customer's job.
The information provided by measuring the residual mass with a point sensor like an ETAC is limited to an average measurement of transfer performance. In addition, because a point sensor typically only measures the transfer efficiency at one isolated location in the cross-process direction, variations that occur across the photoreceptor or transfer belt are not detected by this type of sensor. Therefore, typical ETAC sensors provide only minimal or “gross” information that is employed to control transfer performance.
To overcome this problem, sensors containing arrays of optical sensing elements may be used to sense residual mass across a process direction. In many devices, the array of sensing elements provides information across an entire surface of the photoconductor, transfer belt/web or other surface where residual materials are collected after transfer. Such optical sensing array devices are termed full-width array (FWA) sensors. Such a method eliminates the problem of the point-sensing nature of ETAC residual mass sensors because the residual mass content of the entire image area of the photoreceptor can be captured. However, prior methods were still only concerned with measuring average transfer efficiency. Thus, although the residual mass per unit area value obtained may be more sensitive or accurate than prior point sensors (because it averages over a larger area), such sensing systems do not fully utilize the information that is available from the optical sensor.
The system and method disclosed herein address a need for a residual mass sensor that can sense and record a two-dimensional image or structure (i.e., signature) of the residual mass remaining on a surface after the transfer step in the xerographic process. There also is a need for a residual mass sensor and measurement analysis system/method that may be used to monitor the drift or deviation of residual mass over time (e.g., during a job) that uses the two-dimensional structure of the residual mass image to identify transfer defects that occur over the course of time, including those caused by changes in materials, environment, and print substrates.
One aspect disclosed herein is a closed-loop control system for a xerographic engine that improves print quality (PQ) performance and stability. The disclosed method and system, although directed to monitoring shifts in residual mass, may also take into account the quantified levels of specific print quality defects from the residual mass signature so that a customized and appropriate feedback correction can be made. More specifically, the residual mass signature is sensed after a nominal image is transferred and then monitored by comparison after subsequent image transfer. The difference in the residual mass signature of subsequent images, as compared to the nominal residual mass signature, can be used to detect drift or changes in the process, particularly over a common printing job.
Disclosed in embodiments herein is a method for identifying transfer defects in a xerographic system, comprising: sensing, after image transfer, a nominal residual mass structure on a surface corresponding to a portion of a document rendered within the xerographic system; sensing, after image transfer, a subsequent residual mass structure on the surface corresponding to a similar portion of the same document rendered within the xerographic system; analyzing the difference between the nominal residual mass structure and the subsequent residual mass structure; and detecting a transfer defect, or set of defects, based on the analysis of the residual mass structure.
Also disclosed in embodiments herein is a xerographic output device, comprising: a controller that receives an image signal representing an image to be printed; a photoconductive surface; a charging station that charges the photoconductive surface to a relatively high potential; an exposure station that receives image signals from the controller and records an electrostatic latent image on the photoconductive surface; a development station that deposits toner over the electrostatic latent image on the photoconductive surface to form a toner image; a transfer station that transfers the toner image from the photoconductive surface to a recording medium; a residual mass sensor that senses a nominal residual mass signature after image transfer and a subsequent residual mass signature, and a processor, that receives the nominal residual mass image and subsequent residual mass images and determines a difference between the nominal and subsequent residual mass images to indicate a transfer defect.
Further disclosed in embodiments herein is a method for identifying transfer defects in a xerographic system, comprising: receiving an image signal for rendering; charging a photoconductive surface; exposing the charged photoconductive surface to produce a latent image thereon; developing the latent image on the photoconductive surface; transferring the developed image to a substrate; sensing, after image transfer, a nominal residual mass structure on a surface corresponding to a portion of a document rendered within the xerographic system; repeating the steps above and then sensing, after image transfer, a subsequent residual mass structure on the surface corresponding to a similar portion of the same document rendered with the xerographic system; analyzing the difference between the nominal residual mass structure and the subsequent residual mass structure; and detecting, and possibly quantifying the level of, a transfer defect, or set of defects, based on the analysis of the residual mass structure.